1. Field of the Invention
The present invention relates to a power supply system for supplying power to a computer from a power supply apparatus and a battery and the like, and in particular, to a power supply system capable of making full use of performance of the power supply apparatus.
2. Description of Related Art
In the case of a computer apparatus represented by a notebook-sized personal computer (notebook PC), a power supply apparatus (power supply section), known as an AC adapter, is connected to the computer apparatus, and it can be connected to a commercial power supply by inserting a power plug on a power cord running from the AC adapter into a plug socket for home use. In addition, there are cases where it is configured such that where the power supply apparatus is built into the computer apparatus, it can be connected to the commercial power supply by inserting a power plug on a power cord running from a housing of the computer apparatus into the plug socket for home use.
Typically, the power supply apparatus represented by the AC adapter is generally large and heavy. As a result, it is highly desired that a power supply apparatus be rendered smaller and lighter, especially when considering the portability of the computer apparatus such as the notebook PC. For that reason, in recent years, attempts have been made to render the power supply apparatus smaller and lighter by reducing maximum output power to a level of minimal inconvenience in a normal working condition. By providing a lowered output, the preparation of a large-scale power supply apparatus capable of completely covering maximum power consumption of a system unit of the computer apparatus is avoided.
However, the maximum output power of the power supply apparatus is often lower than the maximum power consumption, so that voltage of the power supply apparatus abruptly drops if the power consumption of the system unit exceeds the maximum output power of the power supply apparatus such as the AC adapter. There has been a recurring operative problem wherein, due to occurrence of this abrupt voltage variation, the voltage supplied to an inverter of a liquid crystal display (LCD) (inverter input voltage) varies and a lamp current varies, creating a constant flickering in the back light of the LCD.
FIGS. 6A and B are diagrams for explaining a conventional method of controlling the maximum power. FIG. 6A shows the maximum power consumption of the system unit, and FIG. 6B shows the conventional method of controlling the maximum power.
Here, for simplification, in a system circuit configuration the maximum power consumption of the system unit of 85 W is divided into a +3.3V logic circuit portion 201 (which is a portion of little load fluctuation), a +5V maximum power portion 202 (which is a portion in which variation of power of HDD, CD-ROM and the like) and a CPU maximum power portion 203 that is a portion of abrupt power variation.
With regard to the maximum power consumption of the system unit of 85 W shown in FIG. 6A, the conventional method of controlling the maximum power is intended to render the AC adapter that is the power supply apparatus smaller and lighter given the maximum output power is 72 W as shown in FIG. 6B. The control method shown in FIG. 6B further secures a margin 207 as a circuit error in current detection for a +3.3V logic circuit portion 204, a +5V power portion 205 and the CPU maximum power portion 206. The +3.3V logic circuit portions 201 and 204 are values acquired from measured values. In addition, it is often a precondition that a CPU constantly spend the maximum power, using a maximum power specification value of Intel Corp. For such condition, it is intended to avoid exceeding the maximum output power of the AC adapter due to the abrupt power variation. Further, given a current value of the +5V power portion 205, if upon detection, a certain current value is reached or exceeded, it is likely that there is a possibility of exceeding the maximum output power of the AC adapter and that power control is performed (for instance, to lower a CPU clock frequency by power management).
Therefore, in the conventional technology shown in FIG. 6B, controls are employed to prevent flickering of the LCD back light for instance, such that power cannot exceed the maximum output power of 72 W of the power supply apparatus even for a moment, as aforementioned. For such a precondition, the conventional technology shown in FIG. 6B is configured to perform a power management function when the power consumption of the system unit becomes 64 W or so since it must secure the margin 207 as a circuit error in current detection and the actual maximum power of the CPU is approximately 80 percent of the maximum power specification. Consequently, the maximum output power of 72 W of the AC adapter as the power supply apparatus cannot be fully utilized and the control is excessively exerted, which results in lower performance of the entire system.